An artificial tear system is provided. The system can be used for various treatments including the treatment of dry eye syndrome, whenever lubrication of the eye is desirable or when the eyes are subjected to dry conditions.
Under normal conditions, ocular fluid forms a thin layer approximately 7-10 .mu.m thick that covers the corneal and conjunctival epithelium. This ultra thin layer provides a smooth optical surface to the cornea by abolishing minute surface irregularities of its epithelium, wets the surface of the corneal and conjunctival epithelium, thereby preventing damage to the epithelial cells, and inhibits the growth of microorganisms on the conjunctiva in the cornea by mechanical flushing.
The tear film normally includes a three layer structure. The outermost layer is a lipid layer derived from the secretions of the meibomian glands and thought to retard evaporation of the aqueous layer. The middle aqueous layer is provided by the major and minor lacrimal glands, and contains water-soluble substances. The inner most mucinous layer is composed of glycoprotein mucin and overlies the corneal and conjunctival epithelial cells. The epithelial cell membranes are composed of lipoproteins and are thus generally hydrophobic. The mucin plays an important role in wetting the surface, as the aqueous solution alone cannot wet this surface. Thus, the mucin provides a hydrophilic surface for the aqueous tears to spread out on and the surface is wetted by a lowering of the tears' surface tension. Under normal conditions, mucin is provided by goblet cells of the conjunctiva and is also provided from the lacrimal gland.
When any of the tear film components is deficient, the tear film will break up, and dry spots will form on the corneal and the conjunctival epithelium. Deficiency of any of the three components (aqueous, mucin or lipid) may result in dryness of the eye. There are many forms of the disease known as keratoconjunctivitis sica. Those connected with rheumatoid arthritis or other connective tissue disease are referred to as Sjogren's syndrome. All of this background information is discussed in the chapter on tears by Tabbara in Vaughan et al., General Ophthalmology, 11th Ed. (1986), pp. 72-77.
It is known to provide a large, solid, artificial tear insert which is placed into the eye. An example of such an insert is sold under the trademark LACRISERT. This rod contains hydroxpropyl cellulose which is slowly released over a period of time in the ocular environment. It is also suggested in Chapter 7 of General Ophthalmology to also apply topical artificial tears to the eye once the inserts are in place.
Not only do these large inserts sometimes cause irritation or blurring of vision, the inserts provide but one material which mimics only one layer of the tear film. The hydroxypropyl cellulose provides the mucin-type material to the tear film. Further, this treatment is not provided in an easy to use suspension form which delivers all of the treatment simultaneously to the eye. The insert must be placed in the eye using special techniques and then artificial tears could be added. The General Ophthalmology book does not discuss the actual composition of the artificial tears which may be added once the solid insert is in place.
As dry eye syndrome can be caused by deficiency of any of the three tear film components, the LACRISERT system does not provide a complete treatment for all cases of dry eye syndrome as all three components of the tear film layers are not present in the LACRISERT system.
It is thus an object of the present invention to provide an artificial tear treatment system which provides all components of the tear film layers. It is a further object to provide a treatment system to treat dryness of the eye successfully by providing all components which will form a tear film mimicking the natural tear film when administered to the eye. Thus, an object is to provide an artificial tear system which compensates for the deficiency of any or all of the natural tear film components, namely aqueous, mucin or lipid.
It is a further object to provide an artificial tear system which can be used any time lubrication is required for the eye or any time the eye is subjected to dryness. Thus, it is an object to provide an artificial tear system which can be used as ophthalmic lubricants, contact lens solutions, gonioscopic lens solutions, and other artificial tear systems.
Further objects include providing an artificial tear system which is easy to administer and which provides an effective delivery of the three components of the tear film.
These objects and other objects are achieved by providing an artificial tear suspension system. The system includes bioerodible mucin-type particles which release mucin-type material when placed in an ocular environment. Lipid-type material is provided which releases lipid-type material when placed in the ocular environment. Further, aqueous-type material is provided which releases aqueous-type material when placed in the ocular environment. The mucin-type particles are suspended in either the lipid-type material or the aqueous-type material or both.
The present invention provides an easy to administer system with effective delivery of all three of the components of the tear film layers. Once administered to the eye, the present invention three component system provides a tear film which perfectly mimics the natural tear film. Further, if natural production of any of the three components of the tear film is deficient, the present system compensates therefore, and thus is a very effective treatment of dryness of the eye, regardless of the cause.